The Advanced Television Systems Committee (ATSC) standard for Digital Television (DTV) in the United States requires an 8-VSB (Vestigial Sideband Modulation) transmission system which includes Forward Error Correction (FEC) as a means of improving system performance. (United States Advanced Television Systems Committee, “ATSC Digital Television Standard”, document A53.doc, Sep. 16, 1995.) FIG. 1 shows a block diagram of a legacy ATSC DTV system comprising transmitter 10 and receiver 20. As shown in FIG. 1, legacy ATSC transmitter 10 includes a data randomizer 111 followed by FEC encoding subsystem 110 having a Reed-Solomon error correction encoder 112, followed by interleaver 114, and trellis encoder 116. The output of FEC encoding subsystem 110 is provided to 8-VSB modulator 119. Legacy ATSC receiver 20 includes 8-VSB demodulator 129 followed by FEC decoding subsystem 120, including trellis decoder 126, byte de-interleaver 124, and Reed-Solomon error correction decoder 122. The output of FEC decoding subsystem 120 is provided to data de-randomizer 121 for re-creation of the input data originally provided to data randomizer 111. The operation of the system of FIG. 1 is described in greater detail in the aforementioned ATSC standard. See also International Patent Application Publication No. WO 2008/144004.
The ATSC DTV transmission scheme is not robust enough against Doppler shift and multipath radio interference, and is designed for highly directional fixed antennas, hindering the provision of expanded services to customers utilizing mobile and handheld (M/H) devices. To overcome these issues, and create a more robust and more flexible system, among other things, it is possible to add a new layer of FEC coding, and more powerful decoding algorithms to decrease the Threshold of Visibility (TOV). The added layer of FEC coding may require decoding techniques such as iterative (turbo) decoding (see, e.g., C. Berrou et al., “Near Shannon Limit Error—Correcting Coding and Decoding: Turbo-Codes (1)”, Proceedings of the IEEE International Conference on Communications—ICC′93, May 23-26, 1993, Geneva, Switzerland, pp. 1064-1070; and M. R. Soleymani et al., “Turbo Coding for Satellite and Wireless Communications”, Kluwer Academic Publishers, USA, 2002) and trellis decoding algorithms like the MAP decoder described by L. R. Bahl, J. Cocke, F. Jelinek and J. Raviv, “Optimal Decoding of Linear Codes for Minimizing Symbol Error Rate”, IEEE Transactions on Information Theory, Vol. IT-20, No. 2, March 1974, pp. 284-287.
In addition, it is possible to include additional training data, also called a priori or preamble data, in the digital data stream to aid the receiver. However, in order to be backward compatible with the original ATSC DTV standard, the additional training data must be introduced prior to data randomizer 101 of legacy ATSC transmitter 10 in FIG. 1. Hence, the training data will be fully encoded by the legacy ATSC transmitter 10. This implies that at the receiver, the data stream must first be decoded with the legacy ATSC receiver to retrieve the additional training data, and then further utilize it to aid the mobile reception.